The invention relates to amine-boranes. More particularly, the invention relates to a method of dehydrogenating amine-boranes. Even more particularly, the invention relates to a method of providing hydrogen for power generation sources, such as fuel cells.
Chemical hydrides for hydrogen storage are being explored as alternatives to high-pressure hydrogen tanks (gas or liquid), sorbents, adsorbed hydrogen, and metal hydride fuels. Chemical hydrides have the potential to be packaged as non-pyrophoric, non-hazardous, solid, or slurried fuels for automotive applications. Hydrogen may then be generated from such hydrides under controlled conditions on-board and on demand. The spent fuel may then be regenerated either on-board or off-board.
Hydrogen storage materials should ideally have high hydrogen content and low molecular weight. Ammonia-borane (H3NBH3), having a molecular hydrogen storage capacity of 19.6 wt %, is therefore an attractive material for such applications. Because the molecule contains both hydridic and protic hydrogen atoms, it spontaneously loses H2 at temperatures above 80° C. Ultimately, H3NBH3 can be dehydrogenated completely, forming ceramic BN, but temperatures in excess of 500° C. are required. Thermal decomposition of ammonia-borane in solution initially affords the cyclic oligomers cyclotriborazane (B3N3H12) and borazine (B3N3H6). It has been demonstrated that preparation of B3N3H6 from H3NBH3 on a large scale can be achieved in high yield over 3 hours by simply heating a tetraglyme solution of ammonia-borane. In addition, it has been shown that borazine can be thermally crosslinked at temperatures as low as 70° C. with concomitant H2 evolution.
It is possible to obtain a large amount of hydrogen from H3NBH3, but low energy (i.e., minimal heat input) methods to utilize this fuel are only just being developed. For example, H2 has been liberated at room temperature from H3NBH3 and the related species dimethylamine-borane (HMe2NBH3) by adding precious metal catalysts. For example, select Rh(I) species dehydrocouple HMe2NBH3 to form H2, along with the cyclic dimer [Me2NBH2]2 and acyclic aminoborane polymers. Phosphine-boranes having the general formula H2RPBH3 (R═H, Ph) also can be dehydrocoupled using metal catalysts to yield acyclic polymers.
Currently, methods of dehydrogenating amine-boranes at low temperature require the use of expensive precious metal catalysts such as rhodium. Therefore, what is needed is a method of dehydrogenating amine-boranes without the use of precious metal catalysts at low temperatures. What is also needed is a metal catalyst for dehydrogenation that can be easily regenerated.